According to an inkjet recording method, high speed recording can be performed with a high freedom degree of imaging pattern and a low noise at the time of recording. Further, image recording can be performed at low cost. Still further, the inkjet recording method has advantages such that color recording can be readily performed. Therefore, recently the inkjet recording method is rapidly spreading and further developing. As a recording liquid for the method, hitherto a dye ink, in which a water-soluble dye is dissolved in an aqueous medium, has been widely used. However, the dye ink is poor in water resistance and weather resistance of the resultant printed article (printed matter). Therefore, studies of the dye ink have been made to improve such disadvantage.
A pigment ink is ordinarily obtained by dispersing a water-insoluble pigment in an aqueous medium. It is general to use a method which includes adding a pigment together with one or plurality of dispersing agents such as various kinds of surfactants or water-soluble polymers to an aqueous solvent, and pulverizing them using a dispersing device such as a sand mill, a bead mill, or a ball mill, to make the diameter of the pigment particle small to fine (see JP-A-2006-57044 (“JP-A” means unexamined published Japanese patent application) and JP-A-2006-328262). Besides, it is proposed to make pigments a solid solution in consideration of improving a coloring force and weather resistance (see JP-A-60-35055). Also disclosed is a method for preparing a pigment dispersion by dissolving an organic pigment and a polymer dispersant or a polymer compound as dispersant in an aprotic organic solvent in the presence of alkali and mixing the solution with water, as a build-up method in which pigment particles and others are made in a liquid-phase (see JP-A-2004-43776). Further, studies have been made of the predetermined polymer compounds per se and the like that are used in the above-described method (see JP-A-2003-26972 and JP-A-2006-342316). However in the build-up method of using a polymer compound as dispersant, it was difficult to dissolve both the pigment and the polymer compound in organic solvent favorably (cosolubilization) and yet to preserve favorable dispersibility of the pigment when the mixture was mixed with water. To solve the problem, a study for balanced cosolubilization and pigment dispersibility by designing a polymer compound having a special structure was carried out (see JP-A-2007-119586). However, further studies should be made for preparation of an industrially valuable high-stability dispersion containing nanometer-sized fine particles that has better general-purpose properties and higher efficient and is produced at low cost.